1. Field of Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. In particular, the invention relates to a semiconductor device suitable for an application of a single chip semiconductor device that is contained in, for example, IC (integrated circuit) cards, and can include a bridge-rectifier circuit, a smoothing capacitor, a nonvolatile memory chip, a CPU (central processing unit), and so on, and also to a manufacturing method of this semiconductor device.
2. Description of Related Art
Recently, IC cards have become increasingly popular for use as individual certification, and electronic money, and the like. The IC cards for these applications contain single chip semiconductor devices that can include bridge-rectifier circuits, smoothing capacitors, nonvolatile memory chips, CPUs, and so on.
In this semiconductor device, a coil antenna, a bridge-rectifier circuit, and a smoothing capacitor compose a power supply circuit section. By receiving magnetic field from outside of the IC card, electromotive force of alternating current appears in the coil antenna. The electromotive force is then full-wave-rectified by the bridge-rectifier circuit, and the rectified voltage is then smoothed by the smoothing capacitor into a constant voltage. The smoothed constant voltage of direct current is supplied to the CPU, the nonvolatile memory chip, and so on as the power supply.
The power supply circuit section mentioned above needs to convert a voltage of alternating current appeared in the coil antenna into a voltage of direct current by the bridge-rectifier circuit in order to perform prosecution of operations, such as an operation of the CPU or writing and reading operations of the nonvolatile memory chip.
FIG. 10(A) is a circuit diagram showing an example of configuration of a bridge-rectifier circuit 80 according to a first related art. As shown in FIG. 10(A), this bridge-rectifier circuit 80 consists of four pn diodes 90a-90d. 
FIG. 10(B) is a cross-sectional diagram showing a structural example of the pn diode 90a built into the bridge-rectifier circuit 80. In FIG. 10(B), a reference numeral 91 denotes a silicon substrate, 93 denotes a p-type silicon (Si) layer, 95 denotes a n-type silicon (Si) layer, 96 denotes a component separation layer, 97 denotes an inter-layer insulation film, 99a and 99b denote aluminum interconnections. An impurity of p-type Si layer 93 is boron whose concentration is around 1020 cm−3. An impurity of n-type Si layer 95 is phosphorous whose concentration is around 1019 cm−3. Other pn diodes 90b-90d not shown in the figures have similar structures to pn diode 90a shown in FIG. 10(B). In the pn diode 90a, an Al interconnection 99a connected to the p-type Si layer 93 acts as an anode terminal, and an Al interconnection 99b connected to the n-type Si layer 95 acts as a cathode terminal.
It is also known that the bridge-rectifier circuit described above can be composed with four MOS transistors instead of the four pn diodes. FIG. 11 is a circuit diagram showing a bridge-rectifier circuit 80′ according to a second related art. Four MOS transistors 90a′-90d′ shown in FIG. 11 are enhancement-type pMOS transistors formed on the silicon substrate and have the same structures.
On the one hand, these MOS transistors 90a′-90d′ have advantages that the forward current can easily be flowed because their threshold levels are easy to be adjusted. On the other hand, pn diodes can be designed to almost prevent the avalanche breakdown by adjusting the impurity concentration. From the above background, bridge-rectifier circuits have been composed of MOS transistors when emphasizing the characteristics with forward bias, or of pn diodes when emphasizing the characteristics with reverse bias.
FIG. 12 shows a band diagram of the pn diode 90a. The left part of FIG. 12 shows the energy band of the p-type Si layer 93, and the right part thereof shows the energy band of the n-type Si layer 95. In FIG. 12, if the p-type Si layer 93 and the n-type Si layer 95 are in the thermal equilibrium state, there is generated a built-in potential φ′. It is known that the value of the built-in potential φ′ is around 1.05 eV. See, for example, Japan laid-open patent publication No. 9-153628.